In general, EVOH resins exhibit excellent transparency, gas barrier properties, aroma retention, solvent resistance, oil resistance, etc. Thus, EVOH resins have conventionally been utilized as films or sheets, such as food packaging materials, medicine packaging materials, industrial-chemical packaging materials, and agricultural-chemical packaging materials, or as molded containers such as tubes, cups, trays, and bottles, so as to take advantage of those properties.
A technique in which a modified EVOH resin that comprises a structural unit having a 1,2-diol at its side chain, which is represented by the following general formula (α), is used in order to improve the melt moldability of EVOH resins is known (see, for example, patent document 1).
[In the formula, X is any bonding chain other than the ether bond; R1 to R4 each independently are any substituent; and n represents 0 or 1.]
Meanwhile, a technique is known in which an EVOH resin composition, obtained by mixing two or more EVOH resins differing in ethylene content, saponification degree, etc. is used for molded products in order to improve the gas barrier properties and melt moldability of EVOH resins. As application of this technique to that technique described above, a technique in which an unmodified EVOH resin is blended with the modified EVOH resin has been proposed (see, for example, patent document 2).
According to this technique, when a layer of the resin composition is laminated to a polyolefin resin layer, a laminate which is reduced in neck-in even when produced through high-speed film formation and which has excellent stretchability and has stable gas barrier properties after stretching can be obtained.
Since EVOH resins are generally used mainly in melt molding, it is preferred that the EVOH resins should be evenly melted by heat and should evenly solidify after molding. However, in techniques in which different EVOH resins are mixed together as described above, the EVOH resins used are different from each other in ethylene content, saponification degree, the kind of modifying group, modification amount, etc. and, hence, the melting points of the EVOH resins differ as a matter of course. Consequently, when such a composition is melt-molded, the components have insufficient compatibility because of the uneven meltability thereof, and there is a tendency that phase separation occurs because the components differ in the rate of solidification. There has hence been a problem that thickness unevenness or streaks occur in molded products obtained from the EVOH resin composition.
As a technique for overcoming that problem, there is a method in which a modified EVOH resin and a normal EVOH resin are separately produced, in which the ethylene content, degree of saponification, and degree of modification of the modified EVOH resin are regulated in advance so as to reduce the melting peak difference between the EVOH resins, and these EVOH resins are then mixed together. In this method, however, the individual resins must be separately manufactured and this tends to impair productivity.
When resins which each have not undergone solvolysis are mixed together and solvolyzed at the same time, this method tends to attain better productivity and result in melting peaks having a reduced difference. However, the melting peak difference is still large, and there has been room for improvement from the standpoint of completely eliminating thickness and streaks in melt-molded products.